In recent years, power line communication (PLC) using a power line for supplying power to electric equipments has been put into practical use. In the power line communication, communication is performed by superimposing a transmission signal having a frequency higher than a commercial power supply frequency on the commercial power.
Since the power line communication is, however, achieved in a communication mode in which a power line to which home electric equipments are connected is used as a transmission line, the quality of the power line communication is sometimes deteriorated due to the effect of the noise of the home electric equipments (also referred to as “home appliance noise”).
Since the effect of this home appliance noise becomes larger near the peak at which the amplitude of a commercial alternating current (AC) voltage waveform reaches its peak, in order to avoid this effect of the home appliance noise, proposed is a technique for performing the power line communication near a so-called zero crossing at which the amplitude of the AC voltage waveform becomes zero (for example, Patent Document 1).